Magnetron tube for the transmission of ultrashort waves



H. GUTTON 2,610,309

MAGNETRON TUBE FOR THE TRANSMISSION OF ULTRASHORT WAVES Sept. 9, 1952 2SHEETSSHEET 1 Filed April 14, 1948 5 m aw MWM 1U.

AGENTS H GUTTON Sept. 9, 1952 MAGNETRON TUBE FOR THE TRANSMISSION OFULTRASHORT WAVES 2 SHEETS-SHEET 2 Filed April 14, 1 48 Hav/ @UTTON' AGENPatented Sept. 9, 1952 .MAGNETRON TUBE FOR THE TRANSMIS- SION'OFULTRASHORT WAVES Henri Gutton, Paris, France, assignor to CompagnieGenerale. de Telegraphic Sans Fil, a corporation of. France ApplicationApril 14, 1948, Serial No. 21,067 In France April 18, 1947 Claims. (01.315-40) This invention relates to tubes serving for the generation orthe amplification of electric oscillations of a ultrahigh frequency, inwhich it is desired, for the purpose of increasing the output, tofavor'an. electromagnetic oscillation of aparticular order in comparisonwith the others, or even to completely eliminate the latter.

The invention relates more particularly to tubes oi'the type calledmagnetrons having a cylindrical anode slit parallel to. the longitudinalaxis or generatrices of thecylind'er,and dividedinto a certain number ofsegments disposed about the cathode.

Heretofore, for the. purpose of obtaining the desired effect, segments,havebeenarranged twobyktwo in. short-circuited relation by means ofconductor tabs, but these means. introduce considerable losses. duetohigh frequency circulation currents in the said connections; moreover,they complicate manufacture and production due to the fact that theyhave to be clamped or welded, which is difiicult to carry out under theconditions of the smallness of the elements concerned.

,The subject of the present invention consists in a process ofmanufacture and inthe construction of such tubes enabling elimination inan associated circuit of all the oscillation, except practically one,without resorting to the hereinbeiore mentioned short-circuitingarrangements, and thereby avoiding the losses and the complication inmanufacture in connection with their employment'. The invention insuresthis resultby giving the-anodicsegments oi 'magnetrons a sectionapproaching the form of equipotentiallines ofthe'electromagneticoscillation of a particular order which is-th'e' only one to beselectively maintained in practice. In order: to obtain such anequipotential surface, the anodicsegment is constructed in a verycharacteristic rounddiorm which clearly distinguishes it from thesharpedge segments of' the anode of classical magnetrons, having edgesformed by the notches al'ong the generatrices of the cylinder providedin, the. body-of the anode.

The invention is also directed. to a process which, for a certain numberofgiven parameters, such as the order of the oscillation to be flavored,the number of segments, the diameter of the cathode and that of theanode, enables, the tracingof" the desired equipotential' lines,andtheree by, the determination of the patterns for the cutting ,of theanodic segments. The latter will have a section resembling the form of ahairpin whose apex is directed toward the cathode, and whose branchesdiverge along the path of the rays is-' suing from the axis of thecathode.

My invention will be more fully understood from the followingspecification by reference to the accompanying drawings, whichillustrate, byway of non-limiting examples, preferred forms of myinvention and wherein:

Figure 1 is a diagram showing the manner of laying out the desiredequipotential surfaces; Fig. 2 represents a fragmentary view of amagnetron whose segments have been prepared according to myinvention,.and in which for the sake of simplicity'the anodic crown andthe cathode which normally have a circular form have-been shown" in astraight" line; Figs. '3 and 4 show modified forms of elements of amagnetron constructed in accordance with my invention and in which thereis shown the connection between the sectioned notches of resonantcavities of various forms ;'=Fig. 5 represents the application of theinvention to magnetrons with overlapping anodic segments; Figure 511represents a partial section of this magnetron along the line 511-511 inFigure 5; and, Fig. 6" represents theap'plication of the invention tomagnetrons.

There will first be considered a classical magnetron operating at anultrahigh frequency and having a cylindrical anode slit parallelly withthe generatrices of the cylinder. Assume that the number of the saidslots is n.

The energy producedbythe'work of the electrons radiates, through theintermediary of the said slots, to the interior of a connected cavity.The presence of slots produces, in the interval separating the cathodefrom the anode, a stationary electromagnetic field, which can be dividedinto two fields of waves, the one travelling in the one direction andthe other in the other direction. The electric field inthis space hastwo components, the one radial and the other tangential. The radialcomponent is maximum when the tangential component. is zero, andconversely.

The continuouszcurrent of the'anode, and the presence of .a magneticvfield, createa movement of rotation ofv the electrons, whose. velocitydepends onthe potential of the. anode, and. the

size of the magnetic'field. When the velocity til the moment at whichthe energy produced.

3 equals the sum of the energies radiated by the oscillator and lost bythe Joule effect in the walls of the circuits.

In general, circuits which are all disposed in series on the path of theelectromagnetic wave constitute an indefinite chain capable oftransmitting an indefinite number of electromagnetic waves circulatingat speeds of rotation, as follows:

r i 2.1 W 311T lnT nT in which T is the period of oscillation.

These different modes of propagation of the electromagnetic Wave furnishbetween the lips of a same slot differences in phase equal to It is ofthe greatest interest to retain only one of these modes of propagationof the electromagnetic field in such away that all the actions of thefield are in phase with the movements of the electrons. There'is usuallyretained only the mode for which the electromagnetic output of the tubeis the best. For the purpose of avoiding the othermodes of propagationthere is a known method for arranging the electrodes into short-circuittwo-by-two by means of strap connections.

It willnow be demonstrated that it is possible, by giving, according tothe invention, the anodic segments a suitable form, to retain only themode of oscillation of the order pi, without resorting to theshort-circuit connections, thereby avoiding high frequency losses, andcomplications in manufacture.

Consider in effect the equation of the electromagnetic field incylindrical coordinates T,a,Z (Fig. '1') and assume, as is usually thecase, that the electric and magnetic vectors are independent of thecoordinate along the axis of the cylinder. Assume, further, the periodwave of pulsation'kc. The cathode may be assumed to be a perfectconductor and, under this assumption, the electric fieldhas notangential components on the surface of radius 1'0 of the cathode.

The general solution for electric and magnetic vectors is of thefollowing form:

to etc;

in which Er is the radial component of the electric vector; EC. is thetangential of the electric vector; Hz is the axial component of themagnetic field, the other components being zero.

K is a constant of integration; Z'pUcr) is a derivative of this functionin relation to Icr; Ap is a coefiicient of amplitude; p represents theorder of the mode propagation, which varies from for the pi to :0 forthe mode corresponding to a cylindrical magnetron without slots. Thesequence of the numbers p is Each solution of the order P must satisfythe condition E=0 on the cathode, from which it results that ,Zp(lcro)=0for all the values of p, This condition determines the value of K.

The amplitudes Ap of each of the waves can be selected in such a Waythat one of the equin 5 corresponding to the mode pi, and the otherwaves will'not be able to propagate themselves. Thus, by calculating theequipotential lines of the field corresponding to the order pi, andemploying one of these equipotential lines as the surface of the anode,there is only retained the'mode pi, to the exclusion of all the othermodes. It is this which constitutes the principle of my invention.

is usually a number sufliciently smaller than 1 that there isonlyretained the first term of the development in series of the functionZpUcr). The components of the electromagnetic field of order then becameas follows: TE,={ L) (2) cos m mo:

.' To T V L E C .rE Km) SlIl p s These ,equations show'that, if [oralways remains sufficiently'smaller than 1, that is, if the perimeter ofthe anodic circumference is small enough for the wave length, then theform and amplitude of the electromagnetic field are independent of thefrequency.

The equipotential lines of, the electric field are represented by theequation:

I (a -e r 1' cos p and their forms areindependent of the frequency. Fig.1 represents the application of this .equa--.

tion to the tracing of the equipotential in the case of a, magnetronwith ten slots (11:10 and p=g=5 The cathode is designated by C; thereference E1 designatesa point on the equipotential, line defined by thecoordinates a and r;. for the angle .1; equals zero cos 'pa becomesequal to 1; and 1' denotes the inside diameter R of theanode. Thisenables determination of the constant A. When the electric field E.

' anodeis; sufiiciently. great compared Withh diameter of: the;cathode.v then the term...

becomes ne l i e T uipc tia lines h come I c smand are practicallyindependent of the diameter of the cathode. I

, Theforegoing equation enablesthe tracing of the. equipotential lines.E1, E2, etc., for any mag.- netronwith slots whose parameters are given,andior any single mode of propagation which it. is desired to, maintain,With the help of these linesas patterns it is. easily possible to traceand cutout the segments in the crown. of the anodic crown, While in'theclassical magnetrons the faces of the segments. turned toward thecathode present a form of circonvolution bounded by sharp edges, the.magnetron according. to this invention presents. rounded edges and thesection. oi segments-resembling the form of a hairpin whose roundedsummit is turned toward the cathode and whose branches are directedtoward the exterior along the asymptotes Y-Y of the equipotential linesas shown in Fig. l. ;Moreover, the magnetron according to my inventionis characterized by the absence of shortcircuiting connections betweenthe anodic-segments. If it-is desired forthe purpose of; eliminating allthe waves-except one, particularly the wave pi, to give the anode. asection identical to the equipotential line, there arethereby alreadyobtainedsatisfactcry results, enabling the shortcircuiting tabs to bedispensedwith, and giving, the said section a rounded form similar tothat of the equipotential lines; Magnetrons-constructed in this wayretain a highoutput, and do not require the employment ofshort-circuiting; .con-

nections,

.In the case of the above calculation the radial wave which" penetratesthrough the slot was assumed to be stationary. Itmaybe regarded'as thesum of two traveling waves. If the slot is terminated at ad by a purelyreactive impedance Z, Fig. 2, it is possible wave in 'thezone whichseparates aa' fromthe cathode, and, for this purpose, it is sufficientfor the impedance to have such a value that the current and the voltagebetween cm are identical with those prevailingin the electromagneticfield in this place. This impedance may be zero, in which case act is ashort-circuit; in this case ca must be disposed at such a distance Mthat is zero, that is, if the following condition, between the abovedetermined Bessel functions, is realized.

When kro is small J 'pUcT'o) is practically zero, in which case M'iscalculated by the equation:

This relation determines the depth M of the radial slits which terminatewhere the field becomes zero.

For the purpose of simplifying the anode it is desirable to terminatethe form of the slot at aa with a purely reactive self-impedance bycutting in the body of the anode a cylindrical cavity to avoiddisturbing the 6. such as..is.,-representedin Fig, 3, in; which; in:dicates. the. magn tic coils. an V e ontain n vesseL;

Starting: at, aa, it would, be possible to connect attheend oftheslot-any other form of cavity serving to give, a suitableself-impedanceat an, Fig. 4. v

The invention is also applicable to magnetrons with resonant segments,in which there-are-employedtwo groups ofoverlapping. segments; the. oneinside the other, and all of them rediating intopa single cavitysurrounding the assembly. Such tubes have been particularly described inFrench Patent No. 835,305, filed March 16, 1938, and French Patent No.839,690, filed December l937, to the present applicant. In the case ofthese magnetrons the slot terminates in the form of an opening at ac andradiates toward the exterior. The impedance occurring between cm iscomplex, and has a real part. The wave which. circulates in the slot isnot stationary- The incidentxwave transports a greater energy than thereflected wave. The movement of the wave, can be. represented by asystem consisting of; a stationary wave plus a fraction of a travelingwave circulating from theinterior toward the exterior; This fractionoi aprogressive wave represents the useful energy.- This energy is furnishedby the work of the electronic charges in the interval between thecathode and the anode. Fig. 5 shows such a magnetron, whichisparticularly described in my patent application Serial No. 759,663,filed July 8, 1947. The segmentsPi belonging, to the one group overlapin the segments-P2 .of the .op

. posite. group presenting an imbricatedappear ance, and theysurround'the cathode. C. Experh. ence shows that it is desirable togive. the; seg: meritsv a bevel in the direction of the cathode. Thesection of these segments is represented in- Fig. 5a.vv giving a partialview in section along 5a=-5.-a. It has been carried-out according tothis invention, but instead of being solidthesesegmentsmay alsobehollow,and at; the same. time. be. given the rounded form. The inventionis ofthe greatest importance-in. this case, because with this typeofmagnetron. the expedient of shortc1rcuiting by means of tabs isentirelydispensed with, and-the modification of the section of thesegments is all that is necessary. to r'eachxa high output: through theelimination of all the.oscil.. lations except one.

Fig. 6. represents another type. of, magnetron, the so-called fiat type,in which the cathode C is flattened instead of rounded, and issurrounded by the anodic segments P-P disposed along a contour which isalso flattened. The latter are given a section according to myinvention. The results obtained are highly important in that theordinary method of short-circuiting by means of tabs becomes superfluouswhen the dimensions of the anodic plane are of the same order ofmagnitude of or greater than the wave length. The anodic slots mayterminate either in a series of cavities connected as with thecylindrical magnetron, or, in the case of the magnetron with resonantsegments, in the interior of a single cavity into which all of the slotsradiate.

I desire that it be understood that the invention is not limited to thetypes of magnetrons herein described but that it is applicable to anymagnetron or any tube, regardless of its function, in which it isdesired to eliminate all the modes of propagation of the electromagneticwave except one, in such a way that all the actions of the field are inphase with the movements of the electrons. The invention covers any tubeserving for the transmission of short waves, and, more particularly,ultrashort waves, in which this result is obtained by giving a suitableform to particularelements, particularly the anodic segments in the caseof the magnetron, which form is similar to or identical with the traceof the equipotential lines at the place of the said elements, in whichthe said lines correspond to the single wave which it is desired tomaintain.

ing a magnetic field parallel to the axis of the cathode.

2. Magnetron comprising in the interior of an air-tight envelope, asingle cathode, an anode surrounding said cathode and comprising aplurality of segments extending towards the cathode, having a sectiondetermined substantially by the equationin polar coordinates r and a! 7I T A (n, (r cos p in which T0 and A are parameters, and p the mode of..propagation of the .Wave produced by said magnetron, and means adjacentsaid magnetron for producing a magnetic field parallel to the axis ofthe cathode.

. 3. Magnetron of the type having cavity resonators .comprising, in theinterior of a gas-tight envelope, a cathode, a single cylindrical anodecoaxial with and surrounding saidcathode, a plurality of slits formed inthe said anode, terminating on the one hand in said cavityresonators'and opening on .the other hand on to the cathode-anode space,said slits defining anodic segments whose section in a planeperpendicular to the cathode axis is substantially in the form of ahairpin whose apex is directed toward the cathode, and means adjacentsaid magnetron for producing a magnetic field parallel to the axis ofthe cathode.

.4. Magnetron of the type having interleaved segments comprisingjin theinteriorofa' gastight envelope, a s'ingle'cyli'ndric'al cathode, twoplane parallel supports perpendicular to the axis of said cathode, eachsupport carrying a certain number of anodic elements extending parallelwith the cathode and symmetrically arranged around it, the segments ofthe two supports being interlaced among themselves and having a'se'ctionin a plane perpendicular to the cathode axis in the form of a hairpinwhose apex is directed toward the cathode, and means adjacent saidmagnetron for producing a magnetic field parallel to the axis of thecathode.

5. Method of making a magnetron tube with split. anodes, said magnetroncomprising a plurality of anodic segments arranged symmetrically arounda single cylindrical cathode of radius re, the said magnetron beingdesigned to oscillate in accordance with the mode 12, said methodcomprising placing a smooth curve of the section of said segment arounda point in the axis 01 said anode taken as a pole, in accordance withthe equation in polar coordinates 1' and a, 1- being the distance of apoint of the curve to said pole and ,a the polar angle of said pointwith respect to the axis of symmetry of said sections:

Y-( A r r sin p in which A is a parameter, embodying the anodic sectionssubstantially in accordance with said smooth curve, and arranging thecathode within the anode thus formed in section so as to make.

its axis coincide with that of the anode.

HENRI GUITON.

REFERENCES CITED The following references are of record inthe file ofthis patent:

UNITED STATES PATENTS

